waterproof concrete

Polymers explained.

This is a deliberately sparse and incomplete explanation.

The main note of caution is: does a polymer work for you if it does not dry?
By polymer we mean a long molecule chain, probably from crude oil originally, that is put into concrete to increase resistance to passage of water through that concrete.

To the best of our knowledge there are two types:
  1. Styrene butadiene rubber (SBR). Many brands.

  2. Bitumen in emulsion / bitumastic. Everdure Caltite.

In more detail:
  1. There are many brands of SBR. To take one, Ronafix, as an example, their BBA certificate states that it is useful as

    • a repair concrete - greater resistance to the passage of moisture

    • a bonding coat - impervious to water under conditions of pressure

    However, clause 16 points out: "Finishing  Once cured and dried ....."

    In my advice for hand mixing waterproof concrete I say that adding some SBR may be useful because if the inside surface of a basement wall ever gets the chance to fully dry out the SBR will form something very like polythene and make the concrete waterproof even if the hand mixing was not accurate or thorough enough to produce otherwise waterproof concrete.

    Years ago, a scientist client seemed very well aware that SBR was hydrophobic and reversed capillary action. If so, typical structural concrete well placed and well compacted would neither visibly leak nor refill with water by capillary action from the side against the ground after an inside surface dried.

    But a supplier of SBR at the time also supplied a PCE plasticiser and, actually, with hindsight it was the PCE that he seemed to express most faith in making the concrete waterproof and not the SBR.

    Another supplier, who in those days sold SBR and a different concrete waterproofer, said he would not use SBR for waterproofing concrete.

    It cannot be avoided that SBR probably has to dry to work as a concrete waterproofer, and a thick member like a basement retaining wall can probably never be relied upon to dry in service.

  2. Everdure Caltite.

    In its favour, bitumen emulsion is one of the chemicals named (Hewlett, 1988; Hewlett 2001*) as a WATER REPELLENT OR HYDROPHOBIC MATERIAL.

    Why then did it not work in research published by the brother of the founder of, and a past technical director of, Cementaid?

    from "The influence of integral water-resisting admixtures on the durability of concrete" 2013. The Concrete Society, p26.

    Aldred (who was once the technical director of Cementaid) has reported the benefits of Caltite in many publications. In one such paper (Aldred, 1987) he reports that in 1984 cores were taken from several old concrete structures located in the tidal and splash zones around Australia. In one structure with 11 years exposure to marine wetting and drying, the plain concrete showed evidence of aggregate exposure and steel corrosion, while the adjacent Caltite concrete (same cement content and water/cement ratio) was in excellent condition.

    The history and development of Caltite is also recorded by Aldred (1988). In another paper (Aldred, 2001) he concluded that the addition of Caltite in concrete with a water/cement ratio of 0.6 generally reduced water transport both when specimens were initially saturated and when specimens were initially dried. However, the use of Caltite in concrete with a water/cement ratio of 0.4 was found to reduce water transport only when the concrete was dried before testing. The fact that the relative improvement over the control concrete was greater under conditions of high water/cement ratio, limited curing and greater degree of drying led the author to suggest that the admixture tended to influence water transport through larger voids and pores, and that Caltite concrete may therefore be relatively insensitive to a certain level of site abuse.

    Aldred also concluded that the use of Caltite may not be effective in reducing water transport for concrete with a low water/cement ratio and no opportunity to dry before exposure, such as diaphragm walls. The diffusion of water vapour through the Caltite concrete was shown to be similar to the control concrete.

    It cannot be avoided that Caltite has to dry to work as a concrete waterproofer, and a thick member like a basement retaining wall can probably never be relied upon to dry in service.

    Perhaps it would work as a water repellent or hydrophobic material if they did not use so much? They add 30 litres, which is 3% by volume of the concrete but almost an additional 20% liquid (much of which is water).

    It does not usually work in the UK in basement construction, although the concrete exceeds C35A and should be watertight.